1. Field of the Invention
The present invention relates generally to telephone line overvoltage protection devices, and, more particularly, to an improved overvoltage protection method and assembly used with a threaded well type protector station.
2. Description of the Prior Art
Overvoltage protection devices are commonly used with telephone lines for protecting telephone equipment against hazardous voltages due to lightning or power surges. Existing threaded well type protector stations typically are used with screw-in or threaded enclosure types of carbon block or gas tube protectors.
Many such known protective arrangements do not provide balanced operation in a failure mode to simultaneously shunt both the TIP and RING to ground. For example, a first carbon block protector having a spark gap formed between opposed carbon electrodes has one of the electrodes coupled to either the TIP or RING of the telephone line pair to be protected and the other electrode coupled to ground potential. A second carbon block protector is connected to the other of the TIP or RING of the telephone line pair to be protected. The first and second carbon block protectors do not provide balanced operation in a failure mode. Gas tube protectors are similarly arranged. Another significant disadvantage of utilizing an inert gas filled overvoltage arrester device is the response time or delay that can take place between the time the voltage surge occurs and the breakdown of the spark gap.
Overvoltage protection circuitry that overcomes many disadvantages of the prior art circuitry is disclosed in McCartney, U.S. Pat. Nos. 4,758,920, issued Jul. 19, 1988, and McCartney et al., 4,941,063, issued Jul. 10, 1990, and both assigned to the assignee of the present invention.
Related U.S. patent application Ser. No. 07/895,380, filed on Jun. 8, 1992, by the present inventor and assigned to the assignee of the present invention and now abandoned, discloses a telephone line overvoltage protection method and apparatus configured as a five-pin plug-in type protector module containing solid-state devices. The disclosed solid-state devices respond to overvoltage conditions on telephone lines faster than gas tube or carbon type arresters and operate in a balanced failure mode to :shunt: to ground both the TIP line and the RING line of a pair of telephone lines when an overvoltage or power surge occurs on either line. A failure mode mechanism of the overvoltage device connects the telephone lines to ground when an abnormal temperature increase results from an overvoltage condition or the like occurs.
A need exists for an overvoltage protection device for use with a conventional threaded well type protector station that overcomes the disadvantages of available devices.